Re: [ATM] Worm mounting

["Don Clement" <clement.focuser@verizon.net>]

>In other words, mechanicals won't compensate telescope and mount flexure
and >atmospherics, electronics can.



Perhaps.and perhaps not.

When bipolar transistor amplifiers were first introduced in high end audio
reproduction a few enthusiasts said that some of the better tube amplifiers
( Marantz, Futterman, Audio Research, modified Dynaco etc.) had a better
sound and that the transistor amplifiers masked some of the more subtle
nuances in sound reproduction. Engineers were quick to point out the
fantastic specifications that the better transistor amplifiers had, almost
non-existent IM distortion and distortion over a wide frequency range. But
the purists insisted that there was something missing and that "tubes"
sounded better. Engineers dismissed this as the tubes were adding distortion
that people must like to hear. (this might have been true with Marshall tube
guitar amps that Hendrix made famous) They again pointed to the testing done
with distortion analyzers and high purity audio generators. Finally, someone
looked at the differences between tube amplifiers and transistor amplifiers.
It turns out that bipolar transistors are very nonlinear devices and that
the tubes used were much more linear devices. The transistor amplifiers were
using massive amounts of negative feedback to get the fantastically low
distortion specifications and the tube amplifiers used much less negative
feedback because of the inherent tube linearity. To measure distortion
engineers used high purity steady state sine wave generators. It turns out
that music has transient components with more than one signal present at a
time. These multiple frequency transients were wiped out when massive
amounts of negative feedback are used with nonlinear devices causing
transient intermodulation distortion that is undetectable using the steady
state sine methods of testing. The point is that telescope mounts and drives
that are not linear have random transients that cannot be totally corrected
using electronics. It is my belief that one start with the smoothest, most
linear mechanical drive possible and then add the closed loop electronics so
that tracking subtleties are not masked or wiped out in the resulting
imaging or strange artifacÚ}ÔÚre not added.



Don Clement

Running Springs, California

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